The Radiation Resources Core Facility serves Cancer Center members by (1) maintaining and operating ionizing radiation-producing devices; (2) training new users in proper operation of the equipment; and (3) keeping records of usage. The facility provides an essential service and has had significant impact on the research of two types of cancer researchers: those studying the cancer-causing and cancer-treating actions of radiation, and those with primary interests in other topics for whom radiation is a useful tool, e.g., for killing cells to prepare feeder layers. Direction for the Facility is the responsibility of Dr. Nancy L. Oleinick, who has been the director since the establishment of the Cancer Center. Day-to-day management is by Mr. John Mulvihill, a radiation physicist who has efficiently operated the facility since 1988. Oversight is provided by a Scientific Advisory Board and by the Cancer Center. The facility is used by cancer researchers from diverse departments and representing all but one of the programs of the Cancer Center. The Cs-137 and Co-60 gamma-irradiators are the primary equipment and together are used 60-80 times per month; representing up to 30 percent and 50 percent of maximum capacity, respectively. In response to requests from users and on the advice of the facility's Scientific Advisory Board, a new low-dose-rate Ir-192 irradiator will be available in a tissue culture incubator, broadening the ability to mimic brachytherapy or chronic environmental exposures. About half of the usage is by Cancer Center members, and most usage (72 percent) supports peer-reviewed, funded research. Since this is the only facility of its type at the university, it must be available to all researchers; however, Cancer Center members who charge their usage to an NIH grant receive a 50 percent discount on their fees. The overall rate of usage indicates that the Core Facility is essential for many cancer researchers.